1. Field of the Invention
The present invention is directed to a radiation detector for an X-ray computed tomography apparatus, of the type having a number of detector modules mounted side-by-side, each module having a sensor array composed of a number of sensor elements.
2. Description of the Prior Art
A detector of the above type is disclosed, for example, in German OS 195 02 574. The known detector has a number of parallel detector lines that proceed in the direction of the axis of a subject, for example a patient, to be transirradiated. Each detector line can be implemented as an assembly unit or detector module. A sensor array formed of a number of sensor elements is thereby accepted on a printed circuit board. The printed circuit board is connected via a flexible section to a further printed circuit board on which a plug for connection to a following evaluation electronics is mounted.
The sensor elements respectively exhibit slightly different properties. In order to avoid image artifacts, it is necessary to calibrate each sensor element. To that end, calibration tables are produced with special measuring devices. The calibration tables contain, for example, information about the temperature behavior, the radiation drift behavior, the relative signal strength, the persistence behavior, the location dependency of the signal strength, the spectral behavior, and malfunctioning sensor elements.
When a detector module fails, the calibration tables must be produced anew overall after the replacement thereof with a further detector module. Due to the considerable time outlay connected therewith and the necessity of special measuring devices, a malfunctioning detector is, according to conventional procedures, not replaced on site. The entire detector is replaced by a new detector and the calibration table is determined for the new detector by processing in the evaluation electronics.
An object of the present invention is to eliminate these disadvantages according to the prior art. In particular, it is an object to provide a detector for an x-ray computed tomography apparatus that is as simple as possible to maintain.
This object is achieved in accordance with the invention, in a detector of the type described above wherein each detector module contains an electronic storage arrangement for storing data for the calibration of each one of the sensor elements. At a replacement of such a detector module, it is no longer required to produce the calibration tables anew. The maintenance of a malfunctioning detector is thus reduced to the simple replacement of a detector module. This saves time and cost.
The electronic storage arrangement can be an ASIC (application-specific integrated circuit). Such a component is available at a relatively low cost.
In an embodiment of the invention, each detector module has a temperature sensor. This makes it possible to calibrate the detector module dependent on the current temperature. The measured results that are supplied are especially precise.
Further, a circuit for digitizing the signals supplied by the sensor array can be provided. This can be another ASIC. In this case, serial signals can be communicated directly from the detector module to the following evaluation electronics. The evaluation electronics can be correspondingly simplified.
The temperature sensor, if used, is formed as preferably a p-n semiconductor junction, and can be a component of the ASIC serving for storage or of the further ASIC. Such a temperature sensor thus can be manufactured in an especially economic way.
The sensor array can be a photo-diode array by a number of photo-diodes. Each sensor element is expediently formed of a photo-diode provided with a scintillator element at the radiation entry side. The storage arrangement is preferably mounted on a printed circuit board that accepts the photo-diode array. The printed circuit board can be connected via a flexible section to a further printed circuit board that accepts a plug. The above features contribute to a compact structure and a simple replaceability of the detector module.
The invention also is directed to an x-ray computed tomography apparatus having an inventive detector module is claimed.